U.S. Central Command officials in Qatar said they are looking into the airstrike.

The Kurds have been engaged in an intense battle with Iraqis in northern Iraq, calling in U.S. airstrikes on Iraqi positions, according to CNN's Jane Arraf, who is traveling with Kurdish fighters near Mosul.

ARRAF: It's been an extraordinary scene behind us. They've been calling in airstrikes almost constantly for the last few hours. These are F-14s dropping 2,000-pound bombs on Iraqi tanks.

It's a bit of a lull. Just a few moments ago, there was an explosion as they targeted another tank. This is just down the road from the scene of that tragedy -- what appeared to be friendly fire. ...

Among the seriously injured [Kurdish fighters] is a senior military commander [Wageeh Barzani], a brother of the key leader of this part of northern Iraq [Kurdistan Democratic Party leader Masoud Barzani].

We also understand that there have been American troops killed in that friendly fire incident. But people on the ground here, the soldiers who treated the injured, said they didn't see any of them.

HEMMER: Any idea how strong the Iraqi forces are on the other side of that line, and is it believed they're regular army or Republican Guard?

ARRAF: It's not clear whether they're Republican Guard or regular army, but what is clear is the tanks that came up [Sunday] morning were enough of a threat that the U.S. forces pulled back somewhat.

They didn't have air cover at the time. When they did get that air support, they managed to go forward again, and they're planning to move positions, to move the front line even further right now. Certainly this daylong battle has been over those tanks dug in.

And they've taken out so far, four tanks, possibly five, as well as armored personnel carriers. There is a significant, threatening military presence very close to here.

EDITOR'S NOTE:CNN's policy is to not report information that puts operational security at risk.